Polyurethane elastomer yarns have been used in diversified field with the excellent physical properties thereof being utilized. However, these yarns pose problems of tackiness, difficulties in taking-up during spinning and a low workability in succeeding steps such as various yarn processings, knitting, weaving, or the like. A measure to solve the above problems has been an approach from application of oiling agents, for example, oiling agents predominantly comprising dimethyl silicone and a metallic soap admixed therewith, oiling agents predominantly comprising mineral oil and a monoamine admixed therewith, or the like (Japanese Patent Publications Nos. 40-5,557 and 46-16,321). However, an improvement through oiling has been recognized to a certain extent but limited and imperfect. Namely, in the case of spinning and taking-up, if the tackiness of the yarns are reduced, the take-up operation tends to be unable to be continued for a long time due to cobwebbing, yarn package collapsing, etc. This tendency becomes conspicuous with an increase of the take-up speed (for example, to 500 m/min. or more) and with a decrease of the diameter of the bobbin (for example, 100 mm or less) during take-up.
On the other hand, if the yarns are made to be tacky, a long time take-up operation will be capable of being conducted, but serious troubles in succeeding steps will occur due to difficulties in yarn unwinding. Alternatively, the application of oil makes textile products uneven due to yarn tension variations caused by white powder deposition onto yarn guides, knitting needles or the like during yarn post-processing and knitting or weaving steps.
As another method for preventing the sticking of yarns, we proposed in Japanese Patent Publication No. 61-14,245, a process for preparing a core and sheath type polyurethane elastomer filament yarn consisting of a polyurethane sheath and a crosslinked polyurethane core. Such a polyurethane core and polyurethane sheath type composite elastomer filament yarn has disadvantages during taking-up at a high speed for a long time on a small diameter bobbin during spinning, unwinding in the axial direction from a bobbin as ordinary nylon or polyester yarns, and yarn handling in succeeding steps. Further, such a yarn is somewhat disadvantageous in heat resistance.
Alternatively, there have been known polyester-based elastomers as a different kind of thermoplastic elastomers. The polyester-based elastomers have been used in diversified fields because of some of the excellent properties thereof and, among other thermoplastic elastomers, have an advantage of being usable in a wide temperature range from high temperatures to low temperatures. Moreover, these elastomers have an improved load-bearing property, a high flexural fatigue resistance and excellent oil and chemical resistances. As with polyurethanes, if the proportion of hard segments is increased, the hardness thereof will increase and the elastic recovery will decrease, while if the proportion of soft segments is increased, the softness and rubbery elasticity will increase but the heat resistance will deteriorate. Elastic yarns obtained from such a polyester-based elastomer are generally required to have a high proportion of soft segments in order to have, an increased elastic recovery which, on the other hand, gives them a poor heat resistance due to a low melting point.
Further, the thus obtained yarns, since they are extremely inferior to ordinary polyurethane elastomer yarns as an elastic yarn, have not yet been put to practical use.
Furthermore, known thermoplastic polyamide-based elastomers, since they are of a light weight and have an excellent shapability, chemical resistance or the like, have so far been used in ,diversified fields, whereas fibers composed of only the elastomer have a poor elastic recovery, when the hard segments are increased and a low heat resistance when the hard segments are decreased as mentioned above, so that it is the present situation that the polyamide-based elastomers have scarcely been commercialized.
Accordingly, crimpable yarns composed of eccentric composite filaments have been reported (for example, in Japanese Patent Application Laid-open No. 58-104,220). However, these filaments themselves do not elongate along their axis and so the elastic recovery thereof as a elastic yarns is poor. Furthermore, the steps necessary to develop crimps in these filaments are so complicate that productivity is not always high.
Furthermore, polystyrene elastomers, which are known as another thermoplastic elastomer, consist of polystyrene hard segments and polybutadiene, polyisoprene or the like soft segments, and exhibit an adequate rubbery elasticity and good low temperature characteristics. However, since they have an inferior heat resistance, polystyrene elastomers have mainly been used as a modifier of engineering plastics and not for forming fibers.
As mentioned above, the polyurethane-based elastomer composite filament yarns as well as other elastic yarns obtained from the above-described thermoplastic elastomers respectively have great disadvantages and serious difficulties.
In the meanwhile, the spinning processes of polyurethane elastomer yarns are generally classified into three processes, i.e., dry-spinning, wet-spinning and melt-spinning processes. Among the other processes, the melt-spinning process has advantages such as a solvent not being required, a high spinning rate and the versatility of apparatuses used therefore, so that it is more advantageous as a commercial manufacturing process.
However, a melt-spinning process, wherein a melt-spinnable thermoplastic polyurethane is used, provides polyurethane elastomer filament yarns having a poor heat resistance and an insufficient recovery from deformation at a high temperature. Further, those yarns present problems of difficulty in unwinding due to the tackiness of the spun and taken-up yarns. In order to solve these problems, the following methods have been proposed:
(1) a method of incorporating a polyfunctional compound during polymerization, etc.; PA0 (2) a method of direct spinning from a polymerization system; PA0 (3) a method of melting a semi-hardened polymer and then extruding the melt at an isocyanate-setting temperature or into a hardening agent; and PA0 (4) a method of conducting a heat treatment after spinning.
In the above, with respect to method (1), crosslinkages sufficient to improve heat resistance raise the melting temperature of the polymer and, accordingly, it becomes necessary to raise the spinning temperature, whereby the spinning is disadvantageously unstabilized.
As to method (2), control of the polymerization reaction is so difficult that problems will occur in dwelling time, heat stability or the like in the course from the polymerization system to the spinning system and, moreover, the resulting yarns having an insufficient heat resistance.
As to methods (3) and (4), though they are effective with respect to heat resistance and recovery from deformation at high temperatures of the polyurethane elastomer yarns, they can be said to be disadvantageous as commercial manufacturing methods due to their high cost since treating apparatuses of a large size are required.
Alternatively, other than the above, we have previously proposed in Japanese Patent Publication No. 58-46,573, a manufacturing process by melt-spinning of polyurethane elastomer filament yarns having an excellent heat resistance. As a result of further assiduous studies of the above proposed process and conjugate-spinning thereof in skillful combination with the aforementioned thermoplastic elastomers (excepting polyurethanes), which have so far been almost neglected in fiber use, we have succeeded in obtaining heat-resistant composite elastic filament yarns which are free from tackiness and have an excellent stretch recovery, and thus reached the present invention.